To charge the batteries of battery-fed devices, such as cellular phones, PDAs, remote controls, notebooks etc., or directly power devices such as lamps or kitchen appliances, an inductive power system enabling a wireless power transfer can be applied. Inductive power systems for transferring power or charging mobile devices are generally known. Such a system comprises a power transmitting device, hereafter called power transmitter, comprising a transmitter coil which can be energized, thereby generating an alternating magnetic field. The inductive power system further comprises a power receiving device, hereafter called power receiver, connectable to, or part of, a device that is to be charged or provided with power. In order to receive the power, the power receiving device is provided with a receiver coil, in which the alternating magnetic field, provided by the energized transmitter coils, induces a current. This current can drive a load or, for example, charge a battery, power a display or light a lamp.
Document US 2009/0108805 describes an inductive battery charging system designed to enable electronic devices to be recharged. The system includes a planar power surface on which a device to be recharged is placed. Within the power surface there is at least one transmitter coil and optionally an array of transmitter coils coupling energy inductively to a receiver coil formed in the device to be recharged. The field of application of such an array may be a general power surface for powering wireless devices, e.g. for charging batteries, integrated in furniture, or as floor or wall covering. The document describes communication from the power receiver to the power transmitter and vice versa. Data transfer from the secondary side (power receiver) to the primary side (power transmitter) may be achieved by modulating a parameter (such as, for example, the loading conditions) on the secondary side. Data transfer from the primary side to the secondary side may be achieved by modulating the excitation of a primary winding, i.e. of the transmitter coil. Data communication may comprise hand-shaking and compatibility checks between the primary side and a load to be charged and/or determination of the charging status of a battery.